Torrential Remote Precipitation of Typhoon Nesat (2022) over the Greater Taipei Area: Dual-polarization Radar Analysis and Ensemble Simulations

Remote precipitation associated with tropical cyclones (TCs) is one of the challenging weather events. Such events are caused by interactions between TC outer circulation and environmental factors such as cold frontal systems or monsoons. The remote precipitation event related to Typhoon Nesat (2022) is characterized by notable differences (e.g., rainfall hotspots, Siberian High and secondary moisture transport) from other cases previously discussed in the literature. Based on the above unique features, the objective of this study is to investigate the mechanisms that lead to torrential and persistent rainfall in the Greater Taipei Area (GTA). Dual-polarization data from the Wufenshan radar reveal distinct precipitation characteristics between the rainband stage (R-stage) and the convergence stage (C-stage). The R-stage features deeper convection, while the C-stage is dominated by enhanced low-level convergence, leading to significant and prolonged precipitation. The results of ensemble simulations based on the Weather Research and Forecasting model highlight the critical role of frontogenesis in driving heavy rainfall in the GTA. Stronger northeasterly winds and a sharper moisture gradient in the Taiwan Strait are positively correlated with rainfall intensity. Additionally, moisture transport along the edge of the monsoon trough (MT) contributes significantly to the event, acting independently of Nesat’s primary circulation. These findings underscore the joint interaction between MT dynamics and local northeasterly flows as a key driver of this torrential remote precipitation event, distinguishing it from mechanisms identified in previous studies. This study provides new insights into the complex interactions between TCs, environmental flows, and mesoscale processes, enhancing understanding of extreme precipitation events in the late TC season in Taiwan.